SQL Conditional Return HAVING

I have been unable to find the WHERE or HAVING condition that helps me return the following:

If a user has activity logged within the past month, I want to return records for the past six (6) months for those users. I have been using the following query so far...

SELECT
    USER, 
    CAST(ACTIVITY AS DATE), 
    COUNT(DISTINCT ACTIONS), 
    SUM(RESULTS)
FROM
    TABLE
WHERE 
    ACTIVITY >= DATEADD(MONTH, -6, GETDATE())
GROUP BY 
    [conditions]
ORDER BY 
    [conditions]

I have attempted to use

HAVING 
    (COUNT(USER) * CAST(DATEADD(MONTH, -1, GETDATE()) AS DECIMAL)) > 0

but I am getting records returns from inactive users who have only logged action within the past six (6) months, not the current or most recent month.

You could use the exists operator with a subquery for the users with activity in the last month:

SELECT
    USER, 
    CAST(ACTIVITY AS DATE), 
    COUNT(DISTINCT ACTIONS), 
    SUM(RESULTS)
FROM
    TABLE a
WHERE 
    ACTIVITY >= DATEADD(MONTH, -6, GETDATE()) AND 
    EXISTS (SELECT *
            FROM   TABLE b
            WHERE  a.USER = b.USER AND
                   ACTIVITY >= DATEADD(MONTH, -1, GETDATE()))
GROUP BY 
    USER
ORDER BY 
    [conditions]